Paperback not so much of the week as of the year, of the decade - or, I am inclined to say, of all time. And why? Because it's the best book ever written, that's why. I use the word "book" with care. It's not a novel, a tract, an epic poem, a history; it is, quite self-consciously, the book to end all books. Made out of all the books that existed in a 17th-century library, it was compiled in order to explain and account for all human emotion and thought. It is not restricted to melancholy, or, as we call it today, depression; but then a true study of it will have to be - if you have the learning and the stamina - about everything. That is why there are about 1,400 pages in this edition, why the only other edition, from Clarendon Press, runs to three volumes (it also costs a bomb compared to this and is, anyway, out of print), and why Burton never, strictly speaking, finished it: there was always something else to go in.

For it is not just Burton's thoughts on the subject of melancholy, but the thoughts of everyone who had ever thought about it, or about other things, whether that be goblins, beauty, the geography of America, digestion, the passions, drink, kissing, jealousy, or scholarship. Burton, you suspect, felt the miseries of scholars keenly. "To say truth, 'tis the common fortune of most scholars to be servile and poor, to complain pitifully, and lay open their wants to their respective patrons... and... for hope of gain to lie, flatter, and with hyperbolical elogiums and commendations to magnify and extol an illiterate unworthy idiot for his excellent virtues, whom they should rather, as Machiavel observes, vilify and rail at downright for his most notorious villainies and vices." And that's a good quote to be getting on with: it shows you that Burton is on the side of the angels, that he's prepared to stick his neck out, and that he is funny.

This last point is important. The lazy browser won't even pick this book off a shelf, let alone open it. When opened at random, it offers not only dense slabs of 17th-century prose, but insane lists that seem to go on for ever, meandering digressions, whole chunks of italicised Latin. The slack browser who gets the gist of the introduction, "Democritus to the Reader" (Democritus was the laughing philosopher; another clue that this is a comedy), will realise that as far as Burton is concerned, everyone on earth is either stupid or mad (himself included). Say that you're taking this on holiday, as poor Alain de Botton did, and you get heaved straight into Pseuds' Corner.

Which is terribly unfair. The only reason you should not take it on holiday is because it will make your luggage too heavy. It is the ideal book to dip into, though. No one on earth is going to expect you to read it cover to cover. (Although I know one person who is doing just that.) It takes only a couple of minutes to get acclimatised to Burton's rhythms and phrasing. Once you do, you realise that he is a rollicking, more-ish writer, from an age that produced the nation's best prose. The Latin is all translated, apart from a bit about the aphrodisiac diet of the Sybarites, as this is a reprint of the 1932 edition. And not only that, but it's useful: it makes you less melancholy. So buy it now.